Intel's Moblin project -- its own sponsored edition of Linux for Atom-powered devices -- just hit the public alpha stage. The Moblin site invites people to take it for a test drive, and that's precisely what I did.
From the outside, Moblin looks a bit like a version of Fedora running XFCE. It boots in a trice from the .ISO image, installs in less than 10 minutes to a system and is quite stable for an alpha, if far from feature-complete. For the sake of testing, I was able to get it running in a virtual machine using VirtualBox, although I needed to enable the IO APIC and PAE/NX options for the VM.
The actual installed version of Moblin also boots amazingly fast -- mere seconds to get to a desktop. Firefox is included, although the included network drivers seem to be a bit flaky; I was only able to get online from a hardwired connection. The only packages listed in Add/Remove Software are the basics that the system installs with; I guess the rest of the packages will be added to the repository later, once everything else is nailed down.
In short, don't run this on a production system, but give it a whirl in its live-CD incarnation, try it out in a VM, and definitely boot it up on that older box in the closet.